In some of the conventionally-known vehicular roof structures provided with a sunroof, a roof panel, having a sunroof opening formed therein, has inner edge portions formed in a closed section so as to increase the strength of the peripheral edge of the opening. One example of such vehicular roof structures is disclosed in Japanese Utility Model Application Laid-Open Publication No. HEI-6-855.
FIG. 9 hereof is a sectional view showing the vehicular roof structure disclosed in the above-mentioned HEI-6-855 publication. According to the disclosure in the publication, inner edge portions of a roof panel 102, opposed to each other in a width direction of the vehicle and defining the peripheral edge of an opening 101 of a sunroof 100, are each bent downward to form a downward bent portion 103 facing the sunroof opening 101, and a flexing plate 106 spans between and fixed to the downward bent portion 103 and a corresponding rail (track member) 104 provided adjacent to the outer side edge of the roof panel 102 so that a closed section 107 is formed by the roof panel 102 and the flexing plate 106.
However, although the provision of the flexing plate 106 can increase the strength and rigidity of the peripheral edge of the sunroof opening 101, it would require an increased number of necessary component parts and increased cost. Further, because each of the bent portions 103 of the roof panel 102 has a downwardly bent cross section and a relatively great height (i.e., vertical width), press-forming corner portions of the opening 101 (i.e, corner portions of the inner edge portions of the roof panel 102) tends to be very difficult. Besides, because the above-mentioned bent portion 103 is not formed at the corner portions, the corner portions would have low strength and rigidity. Further, in order to achieve enhanced product quality, there is another need to reinforce the peripheral edge of the sunroof opening without adversely influencing the outer appearance of the roof panel 102.